hi – we've been discussing what i believe is the same issue here:
the response is not at all encouraging. i'm experiencing the problem using a Dunlop expression pedal converted to MIDI CC with a DB11 Switch Dr.
i have also replicated the problem sending MIDI from Ableton Live – this makes it very easy to document exactly how bad the problem is. I will post pics/video as soon as I have time.
as far as I can tell, Eventide's position seems to be that expecting the H9 to process a dense stream of MIDI is beyond reason, even though it's something that many far less powerful devices can do.